At the club, he found it difficult to break into the first team and was loaned out to J2 League side Oita Trinita at the start of the 2000 season.

After spending two years at Oita, Kaji came back to J1 League in 2002 to play for FC Tokyo.

His club won the 2004 J.League Cup by beating Urawa Reds in the final which ended 0–0 after the extra time.

After eight years with Gamba Osaka, Kaji signed with Major League Soccer club Chivas USA on 24 June 2014.

He missed Japan's first game in the tournament against Australia with Yuichi Komano filling in for his place, but he returned to the team and played in the rest of the competition.

After the 2006 World Cup, Zico was replaced by Ivica Osim who also regularly picked him for the national team.